Mesostructural Mo-, V-based Catalysts:Controllable Synthesis And Catalytic Transformation Of Olefins

Propene is an important organic chemical raw material, and through various reactions (such as polymerization, oxidation, ammoxidation and alkylation, atc.) lots of propene derivatives could be obtained (ploypropene, acrolein, acrylic acid, propene oxide, etc.) which are all intermediates or raw material for various new material and fine chemicals. As the consumption of the downstream products increasing rapidly, it is important to develop a new, green, energy efficient route to produce propene while the traditional propene production process couldn’t meet the increasing demands. In2005, Chauvin, Schrock, Grubbs were awarded the Nobel Chemistry Prize for their great contribution in olefin metathesis, and also brought olefin metathesis back to our vision. The petroleum industry generates large amount of butene and the utilization efficiency of butene stays low, thus to produce high value propene through olefin metathesis reaction has become a promising project. The main topic of this project is the selective oxidation of propene to acrolein, acrylic acid, and propene oxide with high selectivity and conversion. Meanwhile, it is also important to simplify the catalyst components in order to dig the fundamental characteristics of the catalysts and the reaction kinetics. With the growing threat of the global pollution, controlling the pollutants via designing catalysis system operating in low temperature with a great activity is the core of the environmental catalysis research, especially for the elimination of the NOx which does earthshaking harm to the humanity and the global ecosystem balance. In this article, we use the traditional hydrothermal and impregnation method to synthesis well-defined catalyst with highly dispersed or mono dispersed active site. Through modifying the electronic interaction between the active site and the support, we could adjust the dispersion of the active site over the support effectively. Thus we could design a well-structured, high performance mesostructural catalysis system in order to conduct green and highly effective catalytic reaction.1)1-Butene, abundant but inexpensive in industry, can be used to produce more valuable propene and ethene through the well-known metathesis reaction. In terms of catalyst system of molybdena, controlling the interaction between the molybdena and the support is quite crucial. A special support, i.e., well-shaped one-dimensional γ-Al2O3with uniform diameters of～20nm and lengths of-100nm, has been synthesized via oleylamine-assisted hydrothermal method. The molybdena are well controlled in sizes of moderate aggregation suitable for1-butene metathesis with a fairly high rate of propene and ethylene production under mild conditions. The status of MoOx species in the catalyst has been investigated by solid state29Si MAS NMR, Raman, UV-vis, H2-TPR and NH3-TPD techniques. The catalyst, highly stable after twelve times of regeneration, is important for practical utilization for the metathesis reactions.2) Hierarchical Bi2WO6microspheres assembled from single-crystal nanosheets were successfully synthesized by a facile one-step hydrothermal process using polyethylene glycol as the soft template. According to the special properties of bismuth tungstate between energy band and activate of surface oxygen species, the catalytic properties of well-defined hierarchically assembled Bi2WO6nanoflakes with surface dispersed molybdena have been studied with selective oxidation of propene as probe reaction. The adsorption of oxygen causes the decrease in the conductivity of Bi2WO6, demonstrating its nation of n-type semiconductor. The adsorption of oxygen gains electrons from the conduction band of Bi2Wo6to produce oxygen species active for propene reaction at low temperatures, which, however, gives mainly COx as products. The modification by surface molybdena significantly inhibited the total oxidation reaction of propene over the Bi2WO6, while dramatically increased the conversion of propene and selectivity to acrolein simultaneously, without the formation of acrylic acid. This feature is consistent with the requirements of industrial application, the catalysts with simple component and high performance reveal that the controlling the morphology and structure of catalyst is a good idea of designing efficient catalysts system. The characterization of conductivity measurements, H2-TPR, O2-TPD, XPS and C3H6-TPSR indicated that the thermally excited electrons from the Bi2WO6were combined with surface dispersed molybdena and resulted in an extraordinary increase of selective oxidation performance. The unique effects of the hierarchically assembled Bi2WO6nanoflakes on the catalytic property of molybdena were discussed and the mechanism of the catalyst for the selectively catalytic oxidation was proposed.3) A novel one-dimensional TiO2nanowires support with well-defined crystal planes have been synthesized by a facile solution-based hydrothermal method. Two different approaches were used to prepare the high disperse V2O5/TiO2catalyst, incipient-wetness impregnation method using oxalic acid as adjuvant dissolve agent and non-hydrolytic impregnation routes based on nonhydrolytic condensations in nonaqueous media. Selective catalytic oxidation of propene and selective catalytic reduction of NO (NO-SCR) by NH3were used as test reactions to investigate the influence of the synthetic method, of the dispersion degree of active species and of metal oxide-support interactions in V2O5/TiO2catalysts. The V2O5/TiO2(NH) catalyst obtained by surface bonded of organic vanadium species exhibited excellent catalytic properties in the partial oxidation of propene to acetone and NO-SCR by NH3. The physicochemical properties, adsorbed species and surface reaction were investigated by means of N2sorption, XRD, XPS, H2-TPR and in situ diffuse reflectance FTIR spectroscopy (DRIFTS) of NH3sorption-desorption in order to discriminate the effects dispersion degree of active species. It is clearly indicate that vanadium oxide species are highly homodispersed on the surface of TiO2nanowires support when the loading amount of vanadium oxide is≤5.26V nm-2, the V2O5/TiO2(NH) catalyst with vanadium loading amount of2.65V nm-2(4V2O5/TiO2(NH)), which equals to the dispersion capability, possesses a maximum amount of Bronsted acid sites, and easy reduced polymeric state. The catalyst exhibits the best catalytic performance, indicating that surface homodispersed polymeric vanadium oxide species are the primary active species.